cesium133atomet

Cesium-133 is the only stable isotope of the chemical element cesium, with mass number 133 and atomic number 55. In a neutral atom, the electron configuration is [Xe] 6s1. Cesium is a soft, highly reactive alkali metal that occurs in nature predominantly as Cs-133.

Natural cesium consists almost entirely of the Cs-133 isotope, with trace radioactive impurities not forming a meaningful part of its isotopic composition. The nucleus contains 55 protons and 78 neutrons. Cesium-133 has a well-characterized ground-state hyperfine structure, which makes it especially suitable for precise timekeeping and metrology.

The Cs-133 hyperfine transition defines the SI second. Since 1967, the second has been defined as 9,192,631,770 periods of radiation corresponding to the transition between the two hyperfine levels of the Cs-133 ground state. This definition underpins modern atomic clocks and timekeeping systems worldwide.

Applications of cesium-133 include high-precision atomic clocks, which enable accurate timekeeping, GPS synchronization, and telecommunications networks. Beyond timekeeping, cesium is used in research and industry for ion propulsion, vacuum technologies, and various scientific instruments, though its principal global role is in time standards.

Occurrence and production involve mining pollucite-bearing ore, from which Cs-133 is extracted and refined. Major sources include deposits in Canada and Namibia, among others. The element was discovered in 1860 by Robert Bunsen and Gustav Kirchhoff through flame spectroscopy, and its stable isotope Cs-133 remains central to its metrological significance.